Evolution of the N=50 gap from Z=30 to Z=38 and extrapolation towards 78Ni

TL;DR

This paper investigates how the N=50 shell gap evolves with proton number Z from 30 to 38, using experimental mass data and various analysis methods, and extrapolates findings towards the doubly magic nucleus 78Ni.

Contribution

It introduces a comparative analysis of different methods to determine the N=50 shell gap and assesses the impact of correlations, providing a new estimate for 78Ni's shell gap.

Findings

Correlations can bias shell gap measurements, especially with two-neutron separation energies.

The least perturbed methods suggest a specific size for the N=50 gap in 78Ni.

Discussion on whether 78Ni is spherical or deformed based on nucleon interactions.

Abstract

The evolution of the N=50 gap is analyzed as a function of the occupation of the proton f5/2 and p3/2 orbits. It is based on experimental atomic masses, using three different methods of one or two-neutron separation energies of ground or isomeric states. We show that the effect of correlations, which is maximized at Z=32 could be misleading with respect to the determination of the size of the shell gap, especially when using the method with two-neutron separation energies. From the methods that are the least perturbed by correlations, we estimate the N=50 spherical shell gap in 78Ni. Whether 78Ni would be a rigid spherical or deformed nucleus is discussed in comparison with other nuclei in which similar nucleon-nucleon forces are at play.